Control circuits for electric blankets



March 1955 G. c. CROWLEY ETAL CONTROL CIRCUITS FOR ELECTRIC BLANKETS 2Sheets-Sheet 1 Filed July 11, 1951 Inventors. George C. Crowleg,

Rober'fIG Holmes,

Paul A.Cheok,

Their- Attorney.

March 22, 1955 a c CROWLEY ETAL CONTROL CIRCUITS FOR ELECTRIC BLANKETS 2Sheets-Sheet 2 Filed July 11, 1951 Inventors: Gecrge C. Crowley,

Robert G. Holmes,

Paul A.Check,

I 8 Their Attorney.

United States Patent 2,704,803 CONTROL CIRCUITS FOR ELECTRIC BLANKETSApplication July 11, 1951, Serial No. 236,268 9 Claims. (Cl. 219-24))This invention relates to electrically-heated blankets and moreparticularly to the control means used to regulate the current flow tothe heaters for such blankets.

Heretofore, there have been available two types of double-bed electricblankets, namely, the single-control type and the dual-control type. Inthe single-control type, the same temperature is maintained throughoutthe entire blanket, but in the dual-control type, a differenttemperature may be maintained in one half of the blanket than in theother half. The obvious advantage of the dual-control blanket over thesingle-control blanket is, of course, that when two persons are usingthe dual-control blanket, each person may then set the temperature ofhis half of the blanket to his own liking. However, the dual-controlblanket possesses a disadvantage in that it is more expensive than thesingle-control blanket. The difference in cost between the two types iscaused by the fact that the dualcontrol blanket requires two thermalcontrol devices, such as bimetallic cycling controls, while thesingle-control blanket requires only one such thermal control device.

Due to this price differential, persons many times purchase thesingle-control blanket without considering seriously whether it willsatisfy their wants. When, as oftentimes happens, they subsequently findthat for them a dual-control blanket is almost a necessity, their onlyrecourse is to sell the single-control blanket, often at a loss, and buya dual-control blanket. Although at present this inconvenience andaccompanying monetary loss is unavoidable, it could be averted if therewere only some way of converting the single-control blanket to adual-control blanket. The provision of such conversion means would alsobe desirable from the manufacturing point of view, since themanufacturers would then need to make only a single-control blanket anda conversion unit to change it to a dual-controlblanket, rather thanmaking two types of blankets as they now do. i

it is an object of this invention to provide an electric blanket whichmay be simply and easily converted from a single-control unit to adual-controlunit.

It is a further object of this invention to provide a conversion unitfor converting a single-control electric blanket into a dual-controlblanket.

It is another object of this invention to provide a singlecontrolblanket circuit having terminals adapted to receive a quick plug-in typeconversion unit whereby the conversion unit and single-control circuitact together as a dual-control blanket circuit.

The features of this invention be novel are pointed out with pendedclaims. The invention to organization and mode of further objects andadvantages derstood by reference to the be taken in conjunction withings in which:

Fig. l is a schematic diagram of one form of this invention as embodiedin a singlet-control blanket circuit and a conversion unit forconverting, the circuit to a dualcontrol circuit;

Fig. 2 is a schematic diagram of an alternate for'm of this invention asembodied in a single-control blanket circuit which is adapted to beconverted into a dualcontrol circuit;

Fig. 3 is a schematic diagram including the circuit of Fig. 2 in blockform but showing it converted to a dual-control circuit by a conversionunit;

Fig. 4 is a view of a single-control electric blanket together with itscontrol unit and aconversion unit for converting it into a dual-controlblanket, the control which are believed to particularity in theapitself, however, both as operation, together with thereof, maybe bestunfollowing description to the accompanying draw unit and conversionunit embodying a preferred form of this invention;

Fig. 5 is a schematic circuit diagram of the preferred form of thisinvention shown in Fig. 4; and

Fig. 6 is a view of the quick detachable means used to connect togetherthe single-control and conversion units of Figs. 4 and 5.

Referring to Fig. l, therein is shown a double-bed electric blanket 1 inwhich there is arranged, in any of the patterns well known to the art, acombined heating and thermosensitive element 2 such as is disclosed andclaimed in the copending application of Spooner et a1., Serial No.91,396 for Thermo-Sensitive Devices and Apparatus Incorporating the Samefiled May 4, 1949, now Patent 2,581,212, and owned by the GeneralElectrio Company, the assignee of the. present invention. This inventionis illustrated and will be described with respect to blanketsincorporating such a combined heating and thermosensitive element, sincean element of that sort provides the most convenient and reliable meansfor actuating the over-temperature protection circuit customarilyincluded in blanket control circuits. However, the invention is notlimited to such an element, for as will become increasingly obvious, itmay be employed with any sort of resistance heater and blankettemperature sensing element. As shown, the preferred combined heatingand thermosensitive element 2 comprises a first conductor or heaterresistor 3 separated from a second conductor or signal wire 4 by a thinlayer 5 of one of the organic materials disclosed in the aforementionedSpooner et al., Patent 2,581,212, nylon being preferable. The thin layer5 is essentially an insulator at normal operation temperatures of theblanket and is a conductor of electricity at predetermined highertemperatures. I

Otuside the blanket, element 2 is connected to a multiterminal' plug 6having contacts 6a, 6b, 6c, 6d and 6e. Signal wire 4 is connected acrossterminals 6b and 6d, and resistor 3 is connected across terminals 6a and62. The remaining terminal 6c is connected to a tap 7 provided at themidpoint of resistor 3. Moreover, the sections of resistor 3 lyingrespectively between midtap 7 and terminals 6a and 6e are arranged onopposite halves or sides of blanket 1, so that when the blanket is usedto cover two persons, the blanket area over each person is heated by adiiferent section of the resistor. An obvious modification of thiscircuit, of course, would be to use a separate heating andthermosensitive element in each half of the blanket and then connect thetwo elements together so that the same actual circuit exists with twoelements as is illustrated using only one element. Thus, for example, iftwo elements were used, their heater resistors would each have an endterminal common to both and each would have a separate end terminal. Nomatter which is used, the one midtapped heater, or two heaters connectedat their one end to a common terminal, each of the heater sectionspreferably should have a resistance in the order of 135 ohms, if theblanket is to be used with the conventional volt 60 cycle A. C. domesticsupply circuit and such control units as are described hereinafter.

Plug 6 is adzpted to cooperate either with a multiterminal plug-in typereceptacle or socket 8, which has female terminals 8a, 8b, 8c, 8d, 32,and 8 or with a combination plug-and-socket receptacle member 9, whichincludes four combination terminals fin, 9b, 9c, and 9d, each consistingof a female terminal jumpered to a male contact, a separate femaleterminal 9e, and a separate male contact 9f. Plug 6 may be inserteddirectly in socket 8 or may be joined thereto through plug 9.

Socket 8 forms the terminus for a blanket control circuit which ishoused in a control box 10 and is energized by a plug 11 from anyconventional domestic supply circuit. This control circuit bothregulates the current to the blanket heating circuit, i. e., heaterresistor 3, and also serves to de-energize the blanket upon theoverheating of any portion thereof. This overt-emperature protection isprovided by a circuit such as is disclosed and claimed in the copendingapplication of George C. Crowley for Temperature Responsive ControlCircuit, Serial No. 91,402, filed May 4, 1949, now Patent 2,565,478, andalso owned by the General Electric Company, the assignee of the presentinvention. Specifically, the overtemperature protection is provided by arelay 12 whose normally open contacts 13 are connected serially in theblanket heating circuit; and in accordance with the aforesaid CrowleyPatent 2,565,478, the operating coil' 14 of relay 12 is connected to beenergized across opposite output terminals of an impedance bridge, twolegs of which consists of a voltage divider "circuit comprising theserially connected 12,000 ohm resistors 15 and 16 and the other two legsof which'consist of a series resonant circuit comprising in serialrelationship a 0.1 mfd. capacitor 17, signal wire 4, and a 75-henrychoke coil 18, the resistance of signal wire 4 being preferably lessthan 400 ohms.

In order to provide means for connecting signal wire 4 into the resonantcircuit, the ends of capacitor 17 and choke 18 associated therewith arebrought out respec tively to terminals 8d and 8b of plug 8. Thus, nomatter whether plug 6 is joined directly to plug 8 or is joined theretothrough plug 9, signal wire 4 is still connected in the same position inthe resonant circuit. The plug connection used then has no effect on thevoltage supplied to coil 14 and thereby has no effect on the operationof relay 12. For proper operation of the control circuit, the impedanceof coil 14 should be approximately 90,000 ohms with the relay armatureclosed, and relay 12 should pick up with about 130 volts applied to coil14 and should drop out at approximately 75 volts.

The control circuit may be energized by momentarily closing a switch 19which is biased to the open position and manually operable to the closedposition. The closing of switch 19 energizes the resonant circuitdirectly and energizes resistors 15 and 16 through a 12,000 ohm currentlimiting resistor 20. The resistors act as voltage dividers and thus thevoltage available at one output terminal of the impedance bridge isapproximately line voltage. However, due to the series resonant effectof the resonant circuit, the voltage available at the other outputterminal of the bridge, i. e., the voltage across choke 18, risesconsiderably above line voltage. In fact, with a source voltage of 115volts, the closing of switch 19 results in a voltage of about 150 voltsbeing applied to coil 14. This causes relay 12 to pick up, closingcontacts 13 and energizing the heating circuit.

Once relay 12 closes, switch 19 may the impedance bridge is thenenergized through contacts 13. The voltage applied to coil 14 is not asgreat, however, when the bridge is energized through contacts 13 as itis when the bridge is energized through switch 19, because of anautomatic shift in position of resistor 20 from the voltage dividercircuit to the resonant circuit. But under normal operating conditionsof the bridge, the

voltage does not fall off enough to allow relay 12 to .drop

out. The fact that the control circuit is energized is indicated by aneon glow lamp 21, which is energized across the voltage divider circuitthrough a 200,000 ohm current limiting resistor 22.

As previously mentioned, the closing of contacts 13 serves to energizethe blanket heating circuit. According to this invention, however, thethermal control device 23 included in the control circuit may be used,depending upon whether or not plug 9 is inserted between plugs 6 and 8,to control the heating of both sides of the blanket or to control theheating of only one side of the blanket. First, assuming plugs 6 and 8to be direct connected so that terminals 6a, 6b, 6c, 6d and 6e meshrespectively with terminals 30, Sb, 8c, 8d, and 82, the heating of bothsections of heater resistor 3 is then regulated by control device 23.Although various thermal control devices may be employed, the preferredcontrol is of the roomtemperature responsive type described and claimedin the U. S. patent to William K. Kearsley, 2,195,958, April 2, 1940.The temperature regulation is accomplished through a bimetallic cylingswitch member 24, which alternately carries a movable contact 25 intoand out of engagement with a fixed contact 26 in response to the heatsupplied from a 1.35 ohm heater resistor 27 and the surroundingatmosphere. An external control knob 28 is provided to act on switchmember 24 in order that the control may be adjusted to produce variousoperating temperatures of the blanket.

Contacts 25 and 26 form a serial part of the heating circuit, contact25'being connected to one side of the be released, since heating ofopposite halves of the blanket.

power supply line, and contact 26 being connected to the blanket heaterterminals 8a and 86 of plug 3. Specifically, contact 26 is connecteddirectly to terminal 8e but is connected to terminal 8a through heater27.

The third blanket heater terminal 3c of socket 8 is connected in thecontrol circuit to contacts 13. Since the associated terminals 6a, 6eand 6c of plug 6 are connected respectively to opposite ends or"resistor 3 and to its midtap 7, the insertion of plug 6 into socket 8thus connects the two sections of heater resistor 3 in parallel betweencontact 26 and contacts 13. Assuming control 23 to be calling for heat,i. e., contacts 25 and 26 being in engagement, the closing of contacts13 then places the two sections of resistor 3 across the power supply.

Since the resistance of both sections of heater resistor 3 isapproximately one-hundred'times the resistance of resistor 27, theaddition of resistor 27 between one heater section and contact 26 doesnot cause an appreciable difierence in the current flowing in thatsection as opposed to the current flowing in the section connecteddirectly to contact 26. Thus, as switch arm 24 cycles to open contacts25 and 26 in response to the heat from resistor 27, an essentially eventemperature is maintained in both sides of the blanket. In other words,the temperatures on both sides of the blanket are regulated by controldevice 23.

The blanket continues to operate subject to the cycling of switch arm 24until it is tie-energized by the opening of contacts 13. These contactsmay be opened at the discretion of the blanket users by means of'anormallyopen switch 29, which is connected in parallel with capacitor 17and signal wire 4, or they may be opened automatically by the action ofthe control circuit upon an overheat condition of a predeterminedmagnitude occurring in the blanket. Both the manual shut-oft and theautomatic shut-off are accomplished by disturbing the resonance of theresonant circuit, so that the voltage across choke 18 and thus acrosscoil 14 falls 011 to a value insufiicient to keep relay 12 locked in.

Thus, the closing of switch 29 disturbs the circuit resonance byshorting out capacitor 17, while an overheat condition of the blanketdisturbs the resonance by changing the impedance presented by nylonlayer 5. At normal operating temperatures of the blanket, layer 5 isessentially an insulator, but if the blanket overheats to apredetermined cut-otf temperature, as fully explained in theaforementioned patent of Spooner et al., No. 2,581,212, the impedance oflayer 5 decreases sufficiently in magnitude that appreciable currentpasses from resistor 3 to signal wire 4. These current paths formedbetween the resistor and the signal wire efiectively complete parallelcircuits around capacitor 17 and choke 1S and thereby disturb theresonance of the resonant circuit. As mentioned above, this causes thevoltage to decrease across coil 14 so that relay 12 drops out and opensthe circuit. When the blanket, and thus control layer 5, has cooledsufficiently that there are no longer any parallel circuits betweenresistor 3 and signal wire 4 effective to disturb the circuit resonance,the closing of switch 19 will again restore the blanket to normaloperation.

The action of the impedance bridge is exactly the same when plug 9 isinserted between plug 6 and socket 8 because signal wire 4 is stillconnected in the circuit in exactly the same manner. However, theinsertion of plug 9 converts the blanket from a single-temperaturecontrol blanket to a dual-temperature control blanket, i. e., itprovides means for independently controlling the For that purpose, incontrol box 10, terminal 8 of socket S is connected to the line side ofswitch 23, while in plug 9 a room-temperature responsive cycling control30 is connected between terminals 9 and 9e. In other words. when plug 9is placed in the circuit, terminals 641. 6b, 6c and 6d of'plug 6 areconnected in the blanket circuit exactly the same'as before, butterminal 6e is connected to the line through control device 30, ratherthan through control device 23. Thus, the heating of one section ofresistor 3 is still controlled by device 23 but the heating of the othersection is controlled by device 30. Device 30, like device 23, ispreferably of the type disclosed in.

the aforementioned Kearsley Patent 2,195,958 and has a bimetallic switcharm 31 which carries a contact 32 into and 91 1 of engagement with afixed contact 33, in response to the heat supplied from a 1.35 ohmheater resistor 34 and the surrounding atmosphere. Resistor 34 isserially connected with contacts 32 and 33 and the heating circuit ofthe associated side of blanket 1, so that the. cycling of switch arm 31controls the temperature of that side of the blanket. The control deviceis housed in a separate box and an external adjusting knob 36 isprovided to act on switch arm 31 to supply means for adjusting theswitch arm to open the contacts at various blanket temperatures.

Thus, in this first form, the invention provides means whereby anelectric blanket may be converted from a single-control blanket to adual-control blanket merely by the insertion of a special plug betweenthe plug and socket ordinarily used to join the blanket to thesinglecontrol device.

An alternate form of this invention, as embodied in a single-controlelectric blanket and a conversion unit therefor, is illustrated in Figs.2 and 3 of the diagram. The same blanket heating element and the sameovertemperature protection circuit are used in this form of theinvention as were employed in the form shown in Fig. l, and henceidentical members in the two forms are labeled with identical numbers.Thus, in Fig. 2, a combined heating and thermosensitive element 2 isarranged in a blanket 1 in the same manner as in Fig. 1, so that theheater resistor 3 is divided by midtap 7 into two sections disposed onopposite sides of the blanket. Outside the blanket, element 2 isconnected to a S-terminal plug having male contacts 411a, 40b, 40c, 40dand 402, signal wire 4- being connected across terminals 400 and 402,resistor 3 being connected across terminals 40a and 49b, and midtap 7being connected to terminal 4003. Adapted to receive plug 411 is a7-terminal plug-in type receptacle or socket 41, having terminals 41a,41b, 41c, 41d, 41a, 41], and 41g, the five terminals of plug 40 beinginserted respectively in the upper five terminals 41a through 41e ofsocket 41 when the blanket is operated as a single control unit. Asabove, the control circuit includes a relay 12 whose coil 14 isenergized across an impedance bridge, two legs of which comprise matchedresistors 15 and 16, and the other two legs of which comprise a resonantcircuit including capacitors 17, choke 18, and signal wire 4. Terminals41c and 41e are connected respectively to choke 18 and capacitor 17 sothat the joining of plug 40 and socket 41 completes the resonantcircuit. The blanket heating circuit is likewise completed through plug44) and socket 41, midtap 7 of resistor 3 being joined to one side ofthe power source through 1 terminal 41d and contacts 13 of relay 12, andthe ends of resistor 3 being joined to the other side of the linethrough terminals 41a and 41b respectively and a room temperatureresponsive control device 42.

Device 42 is preferably of the type control device disclosed in theaforesaid Kearsley Patent 2,195,958, and here includes a bimetallicswitch arm 43 which carries a movable contact 44 into and out ofengagement with a fixed contact 45 in response to the total heatsupplied from a 0.34 ohm heater resistor 46, a 1.01 ohm heater resistor47 and the surrounding atmosphere. An external control knob 48 isprovided to adjust the control to supply different blanket temperatures.Resistor 46 is connected alone between contact 45 and terminals 41a and41b and is connected in series with resistor 47 between contact 45 andterminal 41 Contact 44 is joined to the opposite side of the powersource from contacts 13 and also to socket terminal 41g. A plug 11 isprovided to connect the control circuit to the conventional domesticpower source, and an operation indicating circuit including neon glowlamp 21 and current limiting resistor 22 is provided for indicating whenthe blanket is energized.

As above, the blanket is energized by the closing of the switch 1% andmay be de-energized either manually through the closing of a switch 27',or automatically through a change in the impedance of layer 5 upon anoverheat condition occurring in the blanket. Switch 27 is connected in adifferent position in the circuit than was switch 27, being connecteddirectly across coil 14. However, switch 27 accomplishes the same resultas switch 27 Since when it is closed it shorts out the relay coil andcauses relay 12 to drop out.

When plug 40 is connected in socket 41, as indicated in Fig. 2, controldevice 42 operates to control the temperature of both sides of theblanket, as both sections of the blanket heating circuit are thenconnected in series with contacts 44 and 45 of heater 46. Since heater47 is not connected in the circuit, switch arm 43 cycles in response tothe heat supplied from resistor 46 due to the sum of the currents inboth sections of resistor 3 flowmg therein. Thus, the control circuithoused in control box 10 permits operation of the blanket as asinglecontrol unit.

However, if it is desired to operate the blanket as a dual-control unit,such a conversion may be made, as is illustrated in Fig. 3, by insertingone side of a combination plug-and-socket member 50 having fourcombination terminals 50a, 50b, 50c, and 59d, each consisting of a malecontact jumpered to a female terminal, a male contact 562, and a femalecontact 50 into the lower five terminals 410 through 41g of socket 41,and then inserting plug 41) into the opposite side of member 50. Thecircuit inside control box 10 in Fig. 3 is identical with that insidethe control box in Fig. 2, and in order to obtain the correct blanketconnections with this form of the invention, the respectively jumperedmale and female terminals of member 50 are displaced in numericalposition from one side of member 50 to the other side, as shown. Thus,when member 50 is placed in the circuit, terminal 41c of socket 41 isconnected to terminal 400 of plug 40, terminal 41d to terminal 40d,terminal 41c to terminal 40c, and terminal 41 to terminal 40a. Terminal41g, however, is connected to terminal 40b through a temperatureresponsive control device 30, like that of Fig. 2, connected betweenterminals 50e and 50; of member 50 and housed in a control box 35.

Thus, although signal wire 4 is still connected in the same position inthe resonant circuit, and midtap 7 is still connected through contacts13 to one side of the power source, the connections to the ends ofresistor 3 have been altered. The one end of resistor 3 is now connectedto contact 45 through both resistors 46 and 47, and the other side ofresistor 3 is now completely disconnected from contact 45, beingconnected through control device 30 to the same side of the line ascontact 44. The two heater sections of resistor 3 are essentially inparallel across the power source, but the heating of each is controlledby a separate ambient temperature responsive control device, thetemperature of one section being controlled by device 42 and thetemperature of the other section being controlled by device 30.

In other words, exactly the same result may be accomplished with thisform of the invention as with the firstdescribed form. Specifically, anelectric blanket may be easily and quickly converted from asingle-control blanket to a dual-control blanket by inserting a singleplug-andsocket member in the proper position between the control box andthe blanket itself. As above, equally as good results are obtainedwhether the blanket is operated as a single-control unit or as adual-control unit.

The preferred form of this invention, however, is illustrated in Figs.4, 5 and 6. Once again, the same heating and thermosensitive element 2is arranged in a blanket 1 so that the heater resistor 3 is divided intotwo sections disposed on opposite sides or halves of the blanket. Thevarious leads of element 2 are brought out of the blanket and are runthrough a multi-conductor cord 60 into a control box 61, wherein ishoused a blanket control circuit. If so desired, cord 60 may be severedat some point and a plug-and-socket arrangement mounted on the free endsto provide means for disconnecting the blanket from the control box.Inside the control box, much of the circuit system is identical withthat in control box 10, and the members in box 61 which are identical inconstruction and function to those in box 10 are numbered identically.For example, housed in box 61 except for signal wire 4 is an impedancebridge, two legs of which comprise matched resistors 15 and 15 and twolegs of which comprise a resonant circuit including in serialrelationship a capacitor 17, signal wire 4, and choke 18. The coil 14 ofan electromagnetic relay is connected to be energized across the outputterminals of the bridge, and the normally-open contacts 13 are connectedserially in the blanket heating circuit. Relay 12 is actuated in exactlythe same manner as in the other two forms of the invention and, asabove, drops out to clear the circuit when switch 27 is closed or whenan overheat condition '7 occurs in the blanket. The operation indicatingcircuit is also identical with that housed in control box 10.

The blanket heating connections, however, are somewhat difierent in thisform of the invention. Thus, the lead from one end of resistor 3 isconnected to an electrically conducting spring arm 62, which is mountedin a plug-in type receptacle or two terminal jack 63, and is normally inengagement with a contact 64. Contact 64 is in turn connected to contact26 of thermostatic control device 23. Also connected to contact 26, butthrough heater 27, is the opposite end of resistor 3. Thus, both ends ofthe resistor are connected to one side of the line through the contactsof control device 23, while the midtap 7 of the resistor is connected,as before, to the other side of the line through contacts 13.

The blanket may then be operated as a single-control blanket withsubstantially identical heating in both sides of the blanket. Thecycling of the bimetallic switch arm 24 is actually, however, responsiveto the current in only one side of the blanket since its actuatingheater 27 is connected in the circuit. of only one of the two sectionsof resistor 3. However, since the resistance of heater 27 is negligiblecompared with that of the sections of resistor 3, its connection in onesection and not in the other does not cause any appreciable differencein the heating of the two sides of the blanket.

In order that the blanket may be operated as a dualcontrol unit, aconnection is provided between the side of the power source associatedwith contact and a spring arm which is mounted in jack 63. As 18 moreclearly shown in Fig. 6, jack 63 includes a pair of electricallyinsulating sockets 66 and 67, which are adapted to receive the maleterminals 68 and 69 of a plug 70. The rounded ends of spring arms 62 and65 extend respectively into sockets 67 and 66 through apertures providedin the socket walls, and are forced out of the sockets as plug isinserted therein. A circumferential groove is provided on each of theterminals 68 and 69 and upon plug 70 being fully inserted into jack 63the rounded ends of spring arms 62 and 65 move into these grooves toretain the plug in the jack. The inserhon of plug 70 removes spring arm62 from engagement with contact 64 and places the section of resistor 3connected to contact 62 in series with a control device 71, which ismounted in a separate box 72 and is connected across terminals 68 and 69by a two-conductor cord 73. S1nce spring arm 65 is joined directly toone side of the line, device 71 and the associatedsection of resistor 3are thereby connected directly across the power source through midtap 7and contacts 13.

Control device 71 is preferably of the room temperature responsive typecontrol disclosed in the aforesa d Kearsley Patent 2,195,958 andincludes a brmetalllc switch arm 74 which carries a movable contact 75into and out of engagement with a fixed contact 76, in response to heatsupplied from a heater resistor 77 and the surrounding atmosphere. Anexternal control knob 78 is provided whereby the control may be adjustedto operate at different temperatures. Control device '71 is thus similarto the other thermostatic control devices described herein and serves toregulate the heating of the associated side of the blanket. 1

Although the insertion of plug 7 0 Into ack 63 cnanges the connectionsof one section of resistor 3, it does not change the connections of theother section which was originally energized from contact 26 throughresistor 27. Therefore, that section of resistor 3 is still controlledby control device 23 and thereby an independent control is provided foreach side of the blanket, device 71 controlling one side and device 23controlling the other. The blanket may thus be converted from asingle-control blanket to a double-control blanket merely by theinsertion of plug 71 into the jacket 63, one particular advantage ofthis form of the invention being that only a two-conductor plug-and-jacksystem is required rather than a 5 to 7 conductor system as in the otherforms illustrated.

Although the various circuits produce satisfactory results using thevalues stated for the various circu t components, these values are meantto be merely illustrative. Obviously, numerous modifications andalterations may be made by those skilled in the art without actuallydeparting from the invention, and it is therefore aimed in the appendedclaims to cover all such equivalent variations as fall within the truespirit and scope of this invention.

.What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination with a blanket, a pair of heaters disposed in oppositesides of said blanket, a power supply for said heaters, connectionsbetween said heaters and said power supply comprising a first thermalcontrol means for both heaters, said means including a multi-terminalsocket and a multi-terminal plug receivable in said socket, a secondthermal control means including a combination plug-and-socket memberadapted to be inserted between said plug and said socket, saidcombination member being so arranged as to disconnect said first controlmeans from operative relationship with one of said heaters upon beinginserted between said plug and said socket, said combination memberbeing further arranged to connect said second control means to controlonly said one of said heaters.

2. in combination with a blanket, first and second heaters disposed inopposite sides of said blanket, each of said heaters having an endterminal common to both and each having a separate end terminal, a pairof power supply terminals for said heaters, a multi-terminal socket anda multi-terminal plug adapted to be received in said socket, aconnection between one of said supply terminals and said common terminalincluding said socket and said plug, a first thermal control device,connections between said separate end terminals and the other of saidsupply terminals including said plug, said socket, and said firstthermal control device to cause said device to control both heaters, acombination plug and socket adapted to be inserted between said plug andsaid socket and adapted upon insertion therebetween to break theconnection between the separate end terminal of said second heater andsaid first control device to cause said first control device to controlsaid first heater only, a second thermal control device connected tosaid combination member to complete a circuit between said separate endterminal of said second heater and said other supply terminal on theinsertion of said combination member between said plug and said socket,said second control device thereupon to control said second heater.

3. In combination with a blanket, a pair of heaters disposed in oppositesides of said blanket, each of said heaters having an end terminalcommon to both and each having a separate end terminal, anovertemperature signal wire disposed in said blanket, a S-contact plughaving separate contacts connected respectively to each of said separateend terminals, said common terminal and each of the ends of said signalwire, a first thermal control device, a six-terminal socket adapted toreceive said plug contacts in a predetermined 5 terminals thereof. theterminal of said socket connected through said plug to said commonterminal being connected to one of said supply terminals, the terminalsof saidsocket connected through said plug to said separate end terminalsbeing connected to the other of said supply terminals through said firstcontrol device to cause said first control device to control bothheaters, and the odd terminal of said socket not engaged by said plugbeing connected directly to said other supply terminal, a second thermalcontrol device, a combination plug and socket member having four plugcontacts jumpered respectively to four socket terminals, a separate plugcontact and a separate socket terminal, said second thermal controldevice being connected between said separate socket terminal andseparate said plug contact, said combination member adapted to beinserted between said plug and said socket member to engage the contactsof said plug and a pre-arranged 5 terminals of said socket includingsaid odd socket terminal, the insertion of said combination member beingeffective to disconnect one of said separate end terminals from saidfirst terminal device and to connect said terminal through said secondthermal control device to said other supply terminal, said first controldevice thereupon controlling one heater only and said second controldevice controlling the other heater.

4. In combination with a blanket, a pair of heaters disposed in oppositesides of said blanket, each of said heaters having an end terminalcommon to both and each having a separate end terminal, anoverternperature signal wire disposed in said blanket, a S-contact plughaving separate contacts connected respectively to each of said separateend terminals, said common terminal and each of the ends of said signalwire, a first thermal control device, a 7-terminal socket adapted toreceive said plug contacts in a predetermined terminals thereof, theterminal of said socket connected through said plug to said commonterminal being connected to one of said supply terminals, the terminalsof said socket connected through said plug to said separate endterminals being connected to the other of said supply terminals throughsaid first control device to cause said first control device to controlboth heaters, one of the odd terminals of said socket not engaged bysaid plug being connected directly to said other power supply terminal,and the other of said odd terminals being connected to said other powersupply terminal through said first control device, a second thermalcontrol device, a combination plug and socket member having four plugcontacts jumpered respectively to four socket terminals, a separate plugcontact and a separate socket terminal, said second thermal controldevice being connected between said separate socket terminal and saidseparate plug contact, said combination member adapted to be insertedbetween said plug and said socket member to engage the contacts of saidplug and a prearranged 5 terminals of said socket including said oddsocket terminals, the insertion of said combination member beingeffective to disconnect one of said separate end terminals from saidfirst control device and to connect said separate end terminal throughsaid second thermal control device to said other supply terminal, saidfirst control device thereupon controlling one heater only and saidsecond control device controlling the other heater.

5. In combination with a blanket, a pair of heaters disposed in oppositesides of said blanket, each of said heaters having an end terminalcommon to both and each having a separate end terminal, a pair of powersupply terminals, a two-t rminal jack having a pair of spring arms and afixed contact normally engaged by one of said spring arms, a plug havingcontacts receivable in said jack and adapted to contact said spring armsand remove said one spring arm from engagement with said fixed contact,a pair of power supply terminals, a first thermal control device, asecond thermal control device connected across the contacts of saidplug, a circuit connecting said common terminal of said heaters to oneof said supply terminals, a circuit connecting one of said separate endterminals to the other of said supply terminals through said firstthermal control device, a circuit connecting the other of said separateend terminals to said supply terminals through said fixed contact andsaid one spring arm of said jack and said first control device to causesaid first control device to control both heaters when said plug isremoved from said jack, and a circuit connecting the other of saidspring arms to said power supply terminal whereby said second controldevice controls one of said heaters when said plug is inserted in saidjack.

6. In an electrically heated blanket, a first heater disposed in theblanket for heating one part thereof, a second heater disposed in theblanket for heating another part thereof, a pair of power supplyterminals, a cycling switch having a thermostat member, an adjustabletemperature setting member, a pair of contacts, and a heating coil forthe thermostat member, a first heater circuit connecting the powersupply terminals to the first heater in series with said pair ofcontacts and said heating coil, a second heater circuit connecting thesecond heater to said cycling switch in parallel with the first heaterwhereby both heaters are regulated by the temperature setting of saidcycling switch, a plug receptacle having contacts in said second heatercircuit, a second cycling switch having a thermostat member, anadjustable temperature setting member, a pair of contacts, and a heatingcoil for the thermostat member, and a plug connected thereto havingcontacts which when connected with said plug receptacle disconnects saidsecond heating circuit from said first named cycling switch and connectsit in series with the contacts and heating coil of the second cyclingswitch whereby when said plug is connected to said plug receptacle thefirst heater is regulated by the temperature setting member of the firstnamed cycling switch and the second heater is regulated by thetemperature setting member of the second named cycling switch.

7. In an electrically heated blanket, a first heater disposed in theblanket for heating one part thereof, a second heater disposed in theblanket for heating another part thereof, a pair of power supplyterminals, a cycling switch having a thermostat member, an adjustabletemperature setting member, a pair of contacts, and a heating coil forthe thermostat member, a first heater circuit connecting the powersupply terminals to the first heater in series with said pair orcontacts and said heating coil, a second heater circuit connecting thepower supply terminals to the second heater in series with said pair ofcontacts but in shunt to said heating coil whereby said second heater isconnected in parallel with the first heater through said pair ofcontacts and both heater circuits are regulated by the temperaturesetting member of the cycling switch for the one blanket part, a plugreceptacle having contacts in said second heating circuit, a secondcycling switch having a thermostat member, an adjustable temperaturesetting member, a pair of contacts, and a heating coil for thethermostat member, and a plug connected thereto having contacts whichwhen connected with said plug receptacle contacts disconnects saidsecond heating circuit from the contacts of said first named cyclingswitch and connects it in series with the contacts and heating coil ofthe second cycling switch whereby when said plug is connected to saidplug receptacle the first heater is regulated by the temperature settingmember of the first named cycling switch and the second heater isregulated by the temperature setting member of the second named cyclingswitch.

8. The combination defined by claim 7 wherein said plug receptaclecomprises a pair of normally closed contacts in the second heatercircuit and a contact connected to such second heater circuit in shuntto the contacts of said first named cycling switch, and said plug hastwo terminals one of which separates said normally closed contacts todisconnect the second heater circuit from said first named cyclingswitch and connect one side of it to one side of the second namedcycling switch and the other of. which connects the other side of thesecond heater circuit to the other side of the second named cyclingswitch.

9. In an electrically heated blanket, a first heater disposed in theblanket for heating one part thereof, a second heater disposed in theblanket for heating another part thereof, a pair of power supplyterminals, a cycling switch having a thermostat member, an adjustabletemperature setting member, a pair of contacts, and a heating coil forthe thermostat member, a first heater circuit connecting the powersupply terminals in series with said pair of contacts and said heatingcoil, a second heater circuit connecting the power supply terminals inseries with said pair of contacts but in shunt to said heating coil, aplug receptacle and a plug connecting the first heater circuit to thefirst heater and the second heater circuit to the second heater wherebysaid second heater is connected in parallel with the first heaterthrough said pair of contacts and both heating circuits are regulated bythe temperature setting member of the cycling switch for the one blanketpart, a second cycling switch having a thermostat member, a pair ofcontacts, and a heating coil for the thermostat member, and a plugconnected thereto having contacts which when interposed between saidfirst named plug and plug receptacle disconnects said second heatingcircuit from the contacts of said first named cycling switch andconnects it in series with the contacts and heating coil of the secondcycling switch whereby when said plug is thus interposed the firstheater is controlled by the temperature setting member of the firstnamed cycling switch and the second heater is controlled by thetemperature setting member of the second named cycling switch.

References Cited in the file of this patent UNITED STATES PATENTS2,138,745 Pecker Nov. 29, 1938 2,163,297 Waage June 20, 1939 2,190,225Vollmer Feb. 13, 1940 2,367,014 Finlayson Ian. 9, 1945 2,467,349 VanDaarn Apr. 12, 1949 2,480,827 Armstrong Sept. 6, 1949 2,565,478 CrowleyAug. 28, 1951 2,581,212 Spooner et al. Ian. 1, 1952 FOREIGN PATENTS117,224 Germany Jan. 29, 1901 651,733 Great Britain Apr. 11, 1951

